In a cooling system for vehicles, a compressor compresses a working fluid that does heat exchange with the ambient air into a high-temperature, high-pressure gas and transfers the compressed working fluid to a condenser. The condenser changes the state of the working fluid in a gas state into a liquid state to increase the amount of heat absorption and transfers the working fluid in the liquid state to an expansion valve. The expansion valve expands the working fluid into a low-temperature, low-pressure state and transfers the expanded working fluid to an evaporator. The evaporator causes the low-temperature, low-pressure working fluid to do heat exchange (to absorb the ambient heat), thereby cooling a predetermined space.